Positional sensors with resolution on the order of a few nanometers or sub-nanometers are used in a wide variety of industrial processes, including fabrication of optical disk products, pattern lithography, and a wide variety of other systems. In some applications, however, metrology requirements for nanometer precision position control must be met over large distances, i.e., distances greater than a millimeter. Many products are subject to metrology limitations for standards, measurements, and fabrication position control on a nanometer scale.
Because nanometer scale objects are not directly visible to the human eye or most microscopes, it is difficult for any mechanical system to verify ongoing nanometer scale accuracy during operation. In general, a five percent rule-of-thumb for position control as a fraction of the feature dimension is required of the equipment that is used to create nanometer scale features. For example, conventional optical disk products are mastered with a mastering system position control which regulates the track pitch of the master patterns. Older compact disk (CD) formats with a track pitch of 1.6 microns required track pitch control of 50-100 nanometers and digital video disk (DVD) formats with a track pitch of 0.74 microns required track pitch control of approximately 30 nanometers. As track pitches continue to progress to smaller sizes, conventional control systems will become ineffective.
Interferrometric sensors with significant environmental control and interpolation can give resolution on the order of a few nanometers over distances of meters, but interpolations from wavelength to the sub-nanometer range is non-trivial. Reference gratings or rulers can also be used in some positioning systems with interpolation to obtain precision within a few nanometers, e.g., less than 10 nanometers, depending on the quality of ruling engine and maximum ruling distances. Alternatively, commercially available capacitive sensors can give one nanometer position precision or better, but the range of these capacitive sensors is typically limited to approximately 50-100 microns. For this reason, capacitive sensors have limited use in conventional systems which require precise translation over distances larger than 100 microns.